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Properties of
Atoms
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Atomic Structure Goals
SC3 Students will use the modern atomic theory
to explain the characteristics of atoms.
a. Discriminate between the relative size, charge,
and position of protons, neutrons, and electrons in
the atom.
b. Use the orbital configuration of neutral atoms to
explain its effect on the atom’s chemical
properties.
c. Explain the relationship of the proton number to
the element’s identity.
d. Explain the relationship of isotopes to the relative
abundance of atoms of a particular element.
e. Relate light emission and the movement of
electrons to element identification.
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Matter
Mixture
Substance
Compound
This will
be our
FOCUS
Element
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What is an Element?
• One of the ~116 known “Pure”,
un-cutable substances….that
still retain the properties of that
substance.
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What is an Atom?
• Smallest piece of matter
that still retains the
properties of that matter.
• What are they composed of?
Timeline
Bohr Model- electrons are found only in specific circular paths, or
orbits, around the nucleus.
Electron Cloud Model: Probable locations of electrons.
MODERN:
Quantum Mechanical Model: Mathematical model describing
the behavior of electrons and energy of electrons in various locations
around the nucleus.
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Atomic Structure
Subatomic Particles
• Protons
• Neutrons
• Electrons
Nucleus
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Atomic Structure
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What makes one element different
from another element?
Number of protons.
Atomic Structure
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Atomic Structure
Rutherford’s Gold Foil experiment led
to the discovery of a positive nucleus.
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Protons
Atomic Structure
• Positive Charge
• The number of protons determines
which element it is.
• All elements have different
numbers of protons
• 1 amu
• Composed of quarks
Atomic Structure
Neutron
• Neural charge
• Located in the nucleus
• 1 amu
• Composed of quarks
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• Smallest subatomic
particle.
• 1/1800 the mass of a
proton.
• Orbit nucleus.
• Negative Charge
Atomic Structure
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•Electrons are
found in different
levels around the
nucleus.
•These are called
Energy Levels or
shells.
•Each energy level
also has “sublevels”
or orbitals
Atomic Structure
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Atomic Structure
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Atomic Structure
Electrons are found
in the
Electron cloud
surrounding the
nucleus.
Atomic Structure
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Each Energy Level Can Hold A
Certain Number of Electrons!
Only
TWO
on
the
first
level!
Atomic Structure
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1
Different
atoms
have
different
Energy
Level
Can
Hold A
7 Each
numbers of electrons!
Certain Numbers of Electrons!
Eight
on the
2nd
2n2
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Atomic Structure
Atomic Structure
1
•
Atomic
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Number
• Number of
Protons
Atomic Structure
1
•Atomic Mass
•Sum of Protons
& Neutrons
The # of Protons determines the identity
of an element. All elements have
different number of protons.
1
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How can I find out how many
electrons an atom has?
• Atom= neutral
• So, the number of protons =
electrons.
• Atomic number tells you the
number of protons.................
• So, it also tells you the number
of electrons!
Atomic Structure
• Practice with a friend…………
Quantum Mechanical Model
• Based on quantum theory, which says matter also
has properties associated with waves.
• According to quantum theory, it’s impossible to
know the exact position and momentum of an
electron at the same time. This is known as the
Uncertainty Principle.
• This model of the atom uses complex shapes of
orbitals (sometimes called electron clouds)
– Orbitals: volumes of space in which there is likely to be
an electron.
So, this model is based on probability rather than certainty.
Atomic Orbitals
• An atomic orbital is a region of space in which there
is a high probability of finding an electron.
• Energy levels of electrons are labeld by principal
quantum numbers (n).
• Each energy sublevel corresponds to an orbital of a
different shape, which describes where the electron
is likely to be found.
• Different orbitals have different shapes.
Quantum Numbers
n, l, m, s
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• Describing electron locations
• 4 quantum number.
• 1st-Principle Quantum # = n
– Which energy level the e- is in.
– n= 1-7
(there are only 7 energy levels)
• Max # formula= 2n2
• the larger the value of n, the farther away from
the nucleus and the higher the energy of the
electron.
2nd quantum number=
l
• Describes the shape (orbital)
• Shapes: s, p, d, f
• Each shape “sublevel”
can only have 2 electrons.
• Max electrons in each sublevel:
– s=(1x2)2, p=(3x2)6, d=(5x2)10, f=(7x2)14
# of
sublevels
s & p
S (1),
p (3),
d (5)
# of
sublevels
(shapes)
F (7)
• 3rd quantum number= m
– Describes orientation
in space
– x, y, z
• 4th quantum number= s
– Describes the spin of
the e in the orbital
– Clock or counterclock
• Brain Break
• Clip
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Orbital Filling Diagrams
(3 rules)
1. Aufbau
Principle: eoccupy orbitals
of the lowest
energy first.
p.133 text
2
2
Orbital Filling Diagrams
• Hund’s Rule: one electron in each
orbital, then electrons pair up with
opposite spins.
• Pauli Exclusion Principal: An orbital
may have no more than 2 electrons. 2 ecannot have the same spin in the same
orbital.
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• Practice:
• H, C, Na, S, Ar, K.
Blocks and Sublevels
• We can use the periodic table to predict which sublevel is
being filled by a particular element.
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Electron Configuration Notation
Practice: Write the electron configuration notation.
Name
• Oxygen
• Aluminum
• Chlorine
Atomic Number
8
13
17
Electron Configuration
1s2 2s22p4
1s2 2s22p63s23p1
1s2 2s22p63s23p5
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Electrons and Light Emission
• When atoms absorb
energy, electrons
move into higher
energy levels
(excited state).
• When the return to
their ground state,
the lose energy by
emitting light.
• The light emitted is
a mixture of a
specific frequencies.
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• A quantum of energy is the amount of
energy required to move an electron from
on energy level to another energy level.
• The higher the ground state, the less energy
it take to move to a higher energy level.
Electrons & Light
Emission
• Each frequency
is a different
color.
• When the
frequencies are
passed through
a prism, the
colors are
separated & an
atomic emission • Larger “jump”- more energy- 29
spectrum is
more towards the blue side
created for
• Smaller “jump”- less energythat element.
more towards the red side
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• The flame test is used to visually determine
the identity of an unknown metal or
metalloid ion based on the characteristic
color the salt turns the flame of a bunsen
burner
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Isotopes
Isotopes are atoms that have the same number of
protons and differ only in the number of neutrons.
Most isotopes are stable but radioactive isotopes
are unstable and break down into more stable
forms by emitting particles and energy (radiation).
Radiation can be detected, so radioactive isotopes
are useful as labels in scientific research and
medical diagnostic procedures.
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Let’s Do some practice problems 
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• How do
you find
this
number?
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Calculating Average Atomic
Mass
Percent(%) abundance of isotopes
Weighted average= Mass of each isotope x %
abundance of that element
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Atomic Mass of Magnesium
Isotopes Mass of Isotope Abundance
24Mg
=
24.0 amu
78.70%
= ______
25Mg
=
25.0 amu
10.13%
= ______
26Mg
=
26.0 amu
11.17%
= ______
Atomic mass (average mass) Mg = 24.3 amu
Mg
24.3
54
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Practice
• Gallium is a metallic
element found in small
lasers used in compact
disc players. In a
sample of gallium,
there is 60.2% of
gallium-69 (68.9 amu)
atoms and 39.8% of
gallium-71 (70.9 amu)
atoms. What is the avg.
atomic mass of
gallium?
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• A sample of
boron consists of
10B (mass 10.0
amu) and 11B
(mass 11.0 amu).
If the average
atomic mass of B
is 10.8 amu, what
is the %
abundance of
each boron
isotope?
Practice
Counting Atoms
• The Mole
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The Mole
• For a given molecule (atom), one mole is a
mass (in grams) whose number is equal to
the atomic mass of the molecule (atom)
What is the Mole?
A counting number (like a dozen)
Avogadro’s number (NA)
1 mol = 6.02  1023 items
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The Mole
– 1 mole of molecules has a mass equal to
the molecular weight in grams.
– A mole of carbon-12 atoms has
a mass of just 12 g.
• How many Atoms is that???
• 1 mole = 6.022 x 1023 atoms
Avogadro's number
Amedeo Avogadro (1776-1856)
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Molar Mass

Mass of 1 mole of an element or
compound.

Atomic mass tells the...
 atomic mass units per atom (amu)
 grams per mole (g/mol)
1 atom of C = 12.01 amu
1 mol of C = 12.01 g

Round to 2 decimal places
Molar Mass
Examples
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
lithium
6.94 g/mol

aluminum
26.98 g/mol

zinc
65.39 g/mol
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Molar Conversion Examples
 How
many grams of iron are in
2.25 mol of iron?
2.25 mol Fe 55.85 g Fe
1 mol Fe
= 126 g Fe
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Molar Conversion Examples
 How
many moles of calcium are
in 5.0 g of calcium?
5.0 g Ca
1 mol Ca
40.08 g Ca
= 0.12 mol Ca
Examples
•
1 mole of Na is the number of atoms in 22.9898g
•
22.9898g is the molar mass
•
1 mole H2O is the number of molecules in 18.015 g H2O
•
1 mole H2 is the number of molecules in 2.016 g H2.
Practice:
1. How many atoms are in 1 mol of H?
2. What is the mass of 1 mol of H?
3. How many atoms are in 2 mole of H?
4. What is the mass of 2 mol of H?
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More Practice:
5.
Convert 589 g of Au to moles.
6.
Convert 344 grams of Fe to moles.
7.
What is the mass of 3 moles of KOH?
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Mole Day is October 23rd!